Each year the glass industry loses to landfills millions of pounds of fiber, and resultantly millions of dollars of potential product, because of the inability of scrap or waste product to be recycled. Losses to landfills are especially true for fiber made for use in glass fiber mat, such as that commonly used to provide network support to roofing shingles. The main problem associated with re-use of glass fiber mat scrap or waste product, and specifically glass fiber mat used to provide network support to roofing shingles, is the often heavy coating of resinous organic material on the fiber, which can comprise up to 20 weight % of the product. The resin can be cured (fully polymerized), uncured, or partially cured; its primary functions are to coat the individual glass fibers to provide surface protection, dispersion capability or other functions related to “sizing” of the fibers, and to eventually “glue” or bind the individual fibers together to form the mat. The most common resins used as binders are urea-formaldehyde based. Other resins, such as acrylic or melamine-formaldehyde, are also used in the industry. Some of the waste fibers are generated during production during filament breakouts or in the generation of product that does not meet specifications. Waste product is typically never used to make mat and usually ends up as “basement scrap”—wet, sticky fiber that is sent directly to landfill. Other waste or scrap fiber, which can be somewhat easier to handle as the binder is often cured and the material has some integrity, can be generated during mat production as edge trim, off-specification roll goods, or the result of process upsets.
Very small amounts of waste or scrap fiber that has some integrity, which typically comprises cured binder, can be recycled into a glass melter used in the production of fiber for glass mat. However, the high organic (resin) content of the waste fiber is combustible and upsets the redox control of the furnace of the glass melter. A typical E glass batch used in the production of fiber for glass mat can only handle about 1-2 weight % of resin. Alternatively, fiber could be recycled back into the fiber mat-forming machine, but to do so would require that the fiber be liberated from and undamaged by the resinous binder that coats and holds the fibers together. Coated or bonded fibers cannot be dispersed into the forming waters and would result in unacceptable product if allowed to end up in the final mat product.
Several methods have been used in the past to “de-bond” fiber in waste material. The easiest is incineration, which can burn off resins of any type. However, the high temperatures required for incineration embrittle the fiber and make the fiber useless as feedstock for mat machines. As a result, incinerated fibers must be sent to landfill.
Other methods to “de-bond” fiber in waste material involve extraction of the binder with acid solutions. For example, U.S. Pat. No. 4,300,955 discloses removing a coating of urea-formaldehyde resin from spun fiberglass with an aqueous phosphoric acid solution, with the fiberglass product subsequently rinsed, dried and chopped for reuse. U.S. Pat. No. 6,454,873 discloses a process and apparatus for recovering clean fiberglass and urea formaldehyde from urea formaldehyde treated waste fiberglass, wherein waste fiberglass passes through acid and wash loops in which the recovery takes place. U.S. Pat. No. 6,793,737 discloses a method for reclaiming fiberglass and a resinous residue from resinous fiberglass product, the method comprising first introducing the resinous fiberglass product to a single chamber or multi-chamber washer/extractor machine; an aqueous acid solution is then used to remove the resinous residue from the resinous fiberglass product; the fiberglass portion is then rinsed, dewatered, and stored for later use; at the same time, the resinous residue is recovered by precipitating the resinous residue out of the acid solution bath and separating it using a clarifier; the fiberglass portion is then available for reuse in the glass industry and other end use applications and the resinous residue may then be available for use in many other industries.
While extraction removes binders and coatings, the acid solutions employed also react with the glass fiber surface, especially the glass fiber surfaces of E glass fibers, leaching glass components such as calcium, boron, and alkali from the glass fibers. The net result is embrittlement and weakening of the fibers, such that only limited amounts of fibers can be recycled back into mat-forming processes without compromise to the physical properties of the mat.
Other methods that have been used to create binder-free, recyclable glass fiber include low temperature oxidation, and swelling and peeling away the binder with organic solvents. The former is a very slow and mostly ineffective process, leaving too much of the organic content behind on the fiber, while the latter involves use of large amounts of environmentally hazardous liquids that create a recycle problem in themselves.
What is needed is an effective process for removing organic coatings and binders from glass fiber surfaces in a manner that is both environmentally friendly and does not compromise the integrity or physical properties of the fiber.